Quadrature phase shifting circuit



April 26, 1949. A. MEACHAM QUADRATURE PHASE SHIFTING CIRCUIT 5 Sheds-Sheet 3 INVENTOR LA. MEACHAM I ATTORNEY K at a Original Filed Oct. 5, 1943 A. ME ACHAM QUADRATURE PHASE SHIFTING CIRCUIT- April 26, 1949.

5 Sheets-Sheet 4 Original Filed. Oct. 5, 1943 N in. itH

INVENTOR 'L, A. MEA CHAM ya A 7TORNE r Patented Apr. 26, 1949 QUADRA'EURE PHASE SHIFTIN G CIRCUIT Larned A. Meacham, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. 525., a corporation of New York Original application October 5, 1943, Serial No. 505,024. Divided and this application January 17, 1945, Serial No. 573,194

7 Claims. I

This invention relates to electric wave generating apparatus and particularly to such apparatus for enerating a sine wave the phase of which may be shifted continuously in either direction.

This application is a division of my application Serial No. 505,024, filed October 5, 1943, now Patent No. 2,422,205, granted June 17, 1947.

An object of the invention is to provide a novel circuit arrangement for generating two electric waves one of which is proportional to the derivative of the other.

The invention has been found to be particularly useful in ange or distance indicating apparatus. In a specific range indicating apparatus embodying the invention, herein shown and described for the purpose of illustration, recurrent pulses of energy are radiated to an object, echo pulses are received from the object, and an indication of the distance from the pulse radiator and receiver to the object is produced. To produce this distance indication, means are pro-- vided for generating range pulses which are delayed with respect to corresponding reference pulses by an amount equal to the delay between the radiated pulses and the corresponding echo pulses. There is provided a range indicator which is preferably calibrated to indicate the distance to the object directly, a delay of one microsecond between a radiated pulse and its re ceived echo corresponding to distance of 16 2 yards, approximately. A range indicating apparatus of this general type is disclosed in my copending application Serial No. ($1,791, filed June 22, 1943, now Patent No. 2,422,204 granted June 1'7, 19oz but the apparatus described this application is in some respects an improvement thereover. Portions of the range indicating apparatus shown and described herein may obviously be substituted for corresponding portions of the range indicating apparatus shown and described in said'copending application. There is employed a start-stop circuit, similar to the start-stop circuit of said copending application, upon which areimpressed pulses in synchronism with the radiated pulses for causing the generation of a square voltage wave. This wave has a negative portion starting with the pulse impressed upon the circuit, which portion has a duration equal to or" preferably greater than the maximum delay occurring between the time of radiation of a pulse and the time of reception of an echo of the radiated; pulse. This negative portion is followed by a positive portion which occupies a time interval during which the, circuit is returned to its stable Ill waiting condition ready to be started again by a succeeding pulse. A timing wave generator comprising an antiresonant circuit is started due to the abrupt decrease in potential at the start of the negative portion of the wave from the startstop circuit and the timing Wave is quickly quenched due to the positive portion of the start-stop wave. Two triode electronic devices having their anode-cathode paths in series with the antiresonant circuit are provided for alternately abruptly interrupting, and starting the flow of current through the antiresonant circuit, in response to the square wave from the startstop circuit impressed upon the control electrodes of the triodes simultaneously. A feedback path is provided for maintaining the output voltage of the generator at constant amplitude.

A phase shifter is provided for continuously shifting in either direction, the phase of the wave from the timing wave generator. The phase shifter comprises an improved Wave generating circuit which produces, under control of the timing wave, two voltage waves which are accurately in quadrature and which start coincidently with each timing wave train. The production of a prolonged starting transient, such as is produced by a, simple resistance-capacity phase splitter, is thus avoided. The wave generator employs an electronic device having a high mutual conductance and such an arrangement of re lated impedance elements in its anode-cathode circuit that, when a, varying potential is impressed upon its control electrode, there are produced at the anode and cathode, respectively, potential waves one of which is proportional to the derivative of the other, that at the cathode being an accurate copy of the impressed potential. When the timing wave app-lied to the control electrode is sinusoidal and has an initial phase such that there is no abrupt change in instantaneous potential, there is preferably employed a path comprising inductance and resistance in shunt with respect to each other between the anode and a source of anode current and a, path comprising capacitance shunted by resistance between the cathode and the current source, the first-mentioned resistance being equal to the capacitive reactance and the second-mentioned resistance being equal to the inductive reactance.

The phase shifting circuit also comprises a phase:

shifter condenser, similar to the phase shifting amplified and the amplified wave supplied to a pulse generator which produces a series of alternatel positive and negative sharp pulses which are accurately spaced by a predetermined interval.

An improved pulse selector is provided for generating a pulse which is coincident with a desired one of each group of timing pulses. This pulse selector makes use of a circuit having resistance R and capacitance C of fixed time constant, the charging of the capacitance being initiated in response to the wave front of each negative portion of the square wave from the start-stop circuit. There is provided an electronic device having a plurality of electrodes comprising a cathode, a control electrode and an anode, which device is normally non-conducting and which is made conducting coincidently with one of the timing pulses to cause a selected timing pulse to be generated. The exponentially rising potential due to the charging of the condenser is applied to the control electrode, there is applied to the cathode a potential which is varied by means of a potentiometer, and the timing pulses are superposed on one of these potentials. One of the timing pulses will thus bring the control grid to a sufficiently high potential with respect to the cathode potential to cause anode current to flow and a range pulse to be produced at the anode, the time of s lection of a timing pulse to form a range pulse varying in accordance with the setting of the potentiometer which controls the cathode potential. The'resistance of the potentiometer is non-uniformly distributed to correct for the non-linearity of the potential rise due to the charging of the condenser and the potentiometer shaft is geared to the shaft of a phase shifting condenser in the phase shifter so that the delay between the radiated pulse and the selected timing pulse may be varied continuously.

The range indicating apparatus has a small minimum delay, say about one microsecond. A fixed delay circuit, the delay of which is equal to or greater than this minimum delay of the range unit is preferably included in the radio receiver so that when the transmitted pulses are directly impressed upon the receiver, the resulting pulses from the receiver may be made coincident with the corresponding range pulses from the range unit when the range indicator is set for zero distance. The range pulses are impressed upon one plate and the echo pulses are impressed upon the other plate of a pair of deflecting plates of a cathode ray tube, a linear sweep wave being applied to another pair of deflecting plates for defleeting the cathode ray beam perpendicularly with respect to the deflection due to the field set up -by the first pair of plates. To determine the range of an object. the delay of the range unit is varied until the visible indication due to the range pulses on the screen of the cathode ray tube is in alignment with the indication on the screen due to the echo pulses from the radio receiver. The range of the object from which the echoes are received may then be read on the indicator of therange unit.

If desired, the range pulses which are brought into coincidence with the echo pulses for causing a range indication to be produced may be used together with the echo pulses to control apparatus for automatically controlling the phase shifting condenser and potentiometer of the range indicator to maintain the range pulses and the echo pulses in synchronism. An apparatus of this type is disclosed in a copending application of B. M. Oliver, Serial No. 491,829, filed June 22, 1943.

The invention will now be described with reference to the accompanying drawing in which:

Fig. 1 is a block diagram of a ranging system in accordance with the present invention;

Fig. 2 consists of curves to which reference will be made in describing the invention;

Figs. 3, 4 and 5, when Fig. 3 is placed to the left of Fig. 4 and Fig. 5 is placed to the right of Fig. 4 ,are a schematic view of a range indicator in accordance with the present invention; and

Figs. 6 to 9, inclusive, are diagrams to which reference will be made in describing the invention.

Referring now particularly to Figs. 1 and 2, there is disclosed a range indicating system in which recurring brief pulses of high frequency electromagnetic wave energy are produced by a transmitter Iii and radiated from a directional antenna H toward an object the distance of which is to be determined and in which the wave pulses reflected from the object are received by antenna l2 and detected by a radio receiver l3. An oscillator I i producs a sinusoidal wave having a period somewhat longer than the time required for a radio wave to travel twice the maximum distance to be measured. Starting pulse generator I 5 produces pulses as indicated at a, Fig. 2, at regular intervals, one for each cycle of the sine wave from oscillator [4. It is not essential to the operation of the system, however, that these pulses occur at regular intervals. The starting pulses a which are of very brief duration, say one-quarter microsecond, key the radio transmitter Iii to cause the radiation of corresponding pulses b of high frequency radio energy. The starting pulse generator [5 and radio transmitter Ill may be the same as the impulse generator and radio transmitter described in my copending application supra. The starting pulses a are also impressed upon a range indicator l9 to produce output or range pulses i which are delayed by a desired amount with respect to the starting pulses a. The range indicator has a small fixed minimum delay, about one microsecond, and a delay circuit having a delay at least equal to this minimum delay is preferably included in the radio receiver 13 so that the pulse a from the receiver and the corresponding range pulses z from the range unit may be adjusted to be coincident when the transmitted pulses b are directly impressed upon the radio receiver l3, and when the range indicator is set for zero distance.

The starting pulses a are impressed upon a start-stop circuit it of the range unit for generating a square voltage wave 0 having an initial negative portion El starting coincidently with a starting pul e a and a positive portion [8. The intervals during which the negative portions ll of wave 0 occur mark the active periods of the range indicating apparatus and the intervals during which the positive portions [8 occur mark the quiescent periods of the apparatus when in operation. These active periods remain fixed while the quiescent periods may vary with frequency variations of source M within a limited range.

The voltage wave 0 produced by the start-stop circuit is impressed upon a timing wave generator 29 which generates a succession of trains of constant frequency oscillatory waves d the phase of which may be shifted continuously through a plurality of cycles by turning the handle I26 of a phase shifter 2|. The phase shifted timing Wave, indicated at e of Fig. 2, starts with an abrupt departure from zero to whatever initial instantaneous amplitude corresponds to its phase position. The period of this oscillatory wave, or a phase shift of the wave through a single cycle, corresponds to the time interval required for a radiated wave to travel through a certain distance and for its echo to return through that dist-ance. The distance represented by a single cycle of the oscillatory wave is the velocity of propagation of the radiated pulse divided by twice the frequency of the oscillatory wave. The timing wave e from the output amplifier of the phase shifter 2! is impressed upon a timing pulse generator 22 which produces alternate positive and negative timing pulses f, a pulse being produced at the beginning of each half cycle of the timing wave. The square wave (2 from the startstop circuit and the timing pulses from the timing pulse generator are impressed upon a pulse selector 23 which selects one of the timing pulses of each group of timing pulses which is delayed by a desired interval with respect to the corresponding starting pulse a, as shown at i, Fig. 2. As indicated at g in Fig. 2, an exponentially rising potential 30 having the timing pulses f superposed thereon is impressed upon a control electrode of an electronic device and a potential 37 which may be varied by means of a potentiometer is impressed upon the cathode of the electronic device to cause the selection of a pulse 26 which causes the control electrode potential to increase sufficiently with respect to the cathode potential to cause the flow of anode current through the electronic device. The shaft 34 of the potentiometer of the pulse selector 23 is connected through the gears 24 to the shaft 29 of a phase shifting condenser of the phase shifter so that the change in cathode potential 3? is equal to the change in peak potential of a superposed timing pulse, such as pulse 28, due to the phase shift of the timing pulses, the resistance of the potentiometer being tapered to correct for the curvature of the exponentially rising potential 36. Only one pulse of each group of timing pulses appears at the output of the pulse selector 23, the pulses of each group which follow a selected pulse being blocked by the output amplifier of the pulse selector.

The echo pulses 7' are impressed upon one of the vertical deflecting plates 3! of a cathode ray tube 30 and the range pulses are impressed upon the other vertical deflecting plate. If desired, of course, a step pulse may be produced under control of the selected pulse 2' and impressed upon a vertical deflecting plate of the cathode ray tube for producing a range mark on the cathode ray tube screen as disclosed in my copending application, supra. Any suitable linear sweep wave It may be impressed upon the horizontal deflecting plates of the cathode ray tube 30. As shown, the sweep wave generator is controlled by the starting pulses a from starting pulse generator id to maintain the sweep wave in synchronism with the starting pulses. Alternatively the pulses i could be utilized for controlling the sweep wave generator and pulses which are delayed by a short fixed. period with respect to the pulses i could be used as the range pulses impressed upon a vertical deflecting plate of the cathode ray tube. By rotating shaft 29 of the phase shifter condenser to which the potentiometer of the pulse selector is geared, a range mark produced by range pulses 2' may be caused to travel across the luminescent screen of the cathode ray tube until it is brought into alignment with an echo mark produced by echo pulses 7. The distance to the object from which the echo pulses are received may then be read directly from a revolution counter or range indicator 32 attached to shaft 29.

The range indicating apparatus is shown in greater detail in Figs. .3, 4 and 5 when Fig. 3 its placed to the left of Fig. 4 and Fig. 5 is placed to the right of Fig. 4. A suitable starting pulse generator and radio transmitter are shown in my copending application supra and are therefore not being described in detail herein. The startstop circuit !6 is similar to the start-stop circuit described in said copending application but is designed to prevent the false triggering of the circuit by extraneous pulses of smaller amplitude than that of the starting pulses a. The startstop circuit employs two electronic triodes VI.! and V9.!, triode V!.! having a cathode 4!, a control electrode 32, and an anode 43 and triode 79.! having a cathode M, a control electrode 45 and an anode at. Negative starting pulses a from the starting pulse generator !5 are applied through a SO-micromicrofarad condenser Cl across 0.5-megohm resistor R! which is connected between the control electrode 52 and the grounded cathode fl The anode A3 is directly conductively connected to the control electrode 45 and the anode i0 is connected to the control grid 42 through a condenser C4 the capacity of which is 400 micromicrofarads when a maximum range of 22,000 yards is to be measured. For this range the alternating current source M may have any frequency up to about 4,000 cycles. The cathode 4 is connected to ground through 15,000-ohm resistor R i shunted by a 500-micromicrofarad condenser C6. Anode potential is supplied to the anode G3 from the positive terminal of 300-volt battery 5! through series resistors R8 (1,000 ohms) and 0.1-megohm resistor R3, the negative battery terminal being grounded. Positive voltage from source 5! is supplied to anode 46 through series resistors R8, R! 8,000 ohms) and R6 (18,000 ohms). The positive battery terminal is also connected through series resistors R8 and R5 (56,000 ohms) to the cathode 44. A 50- micromicrofarad condenser C5 is connected in shunt with respect to resistor R6. A filter condenser CB! of 0.1 microfarad is connected between the negative terminal of resistor R8 and ground. A resistor R05 of 1.8 megohms is connected between the negative terminal of resistor R8 and control grid 42 to maintain the grid positive with respect to cathode 4! during quiescent periods and thus to lower the input impedance and prevent false operation of the circuit due to extraneous pulses during this period. The negative pulse 11 applied to the control grid 42 causes the interruption of anode current in triode VLI, to make the potential at anode t3 and at control 45 more positive. Anode current is thus caused to flow in triode V9! Triode VLI con.- tinues to be cut off and V0! continues to be conducting during the active period due to the discharge current of condenser C4 flowing through the anode-cathode path of triode V5 and resistor R! and the resulting negative bias on the control grid 5-2. At the end of the active period. this discharge current and the resulting grid bias reached a sufficiently low value to cause the triode V!.! to pass anode current and during the following quiescent period the condenser cs is again charged through resistors R6 and R! and the control electrodecathode path of triode VI. I. When the triode V9.l becomes conducting, the potential at the common terminal of resistors R6 and R1 becomes less positive with respect to ground and, when the conduction through triode V9.! is interrupted the common terminal of resistors R2 and R1 becomes more positive, thus producing the start-stop wave 0.

The start-stop wave from the start-stop circuit is impressed upon the input circuits of triodes V2.l and V2.2 of the timing wave generator 20. The common terminal of resistors R5 and R! is connected through 0.01-microfarad condenser Cl and 0.01-microfarad condenser C9, to the control electrode of triode V2.2 which is connected through l-megohm resistor R| l to the grounded cathode. The common terminal of resistors R6 and Bi is also connected through condenser Cl and 0.01-microfarad condenser C i S to the control electrode of triode V2.1 which is connected through l-megohm resistor R8 to the cathode.

The anode current paths for triodes V2.i and V2.2 may be traced from the positive BOO-volt terminal through resistor R8, 10,000-ohm resistor RH], the anode-cathode path of triode V21, the antiresonant circuit comprising 3.66-millihenry inductor L2 shunted by 1,000-micromicrofarad condenser CI3 and the anode-cathode path of triode V2.2 to ground. The anode-cathode path of tube V2.2 is shunted by 25-micromicrofarad variable condenser C14. Condenser Ca2- of 0.1 microfarad is connected between the cathode of triode V2.l and ground. The inductance L2 and the condenser Cl 3 are enclosed within a grounded shield 53. This shielded antiresonant circuit is placed in a suitable oven (not shown) the temperature of which is maintained constant in order to avoid frequency variations due to temperature change. During each quiescent period a current of about 10 milliamperes flows in the anode current circuit of triodes V2.! and V2.2, the voltage drop across each of the anode-cathode paths of these tubes and that across resistor Rio being about 100 volts. The interruption of the anode current from the 300-volt source due to the negative portion I! of the start-stop wave impressed upon the control grids of triodes V2.l and V2.2 simultaneously starts the oscillatory timing wave d in the circuit. The oscillatory wave is quenched during the early portion of the quiescent period due to the positive portion I 8 of the start-stop wave applied to the control grids of triodes V2.! and V2.2. The frequency of the timing wave is 81,955 kilccycles which corresponds to a range of 2,000 yards per cycle. When anode current is flowing in the circuit, condenser C32 is charged to about 100 volts and this charge is maintained during the active periods of the range indicator when the triodes V21 and V2.2 are non-conducting. Control of the current by the two triodes, acting simultaneously, results in keeping the potential across CB2 or between the upper end of L2 and ground constant at all times.

In order that succeeding stages of the range unit behave uniformly throughout the active period, the timing wave is sustained at constant amplitude by means of a positive feedback which is conveniently provided through the cathode follower action of the electronic device V3 of the phase shifter circuit, as will be described below. The anode-cathode circuit of this tube may be traced from the 300-volt source through 1,000- ohm resistor R24, inductor L! of 11.64 millihenries in parallel with 6,000-ohm resistor Rli, the anode-cathode path, 10,000-ohm resistor R in parallel with 250-micromicrofarad condenser C15 and -micromicrofarad variable condenser Cl6, to ground. The anode of triode V2.2 is connected through 100-ohm resistor RIG to the control electrode and a mid-tap of inductor L2 is connected through 47,000-ohm resistor RM to the cathode. Screen grid potential is supplied to the tube through 20,000-ohm resistor RIB and 100-ohm resistor R98 with the common terminal of RI!) and R63 connected to the cathode through 0.1- microfarad condenser CH. The tube V3 has a high mutual conductance and the impedance between the cathode of V3 and ground is sufficiently high to cause the alternating component of the potential at the cathode with respect to ground to be an accurate copy of the potential at the control grid with respect to ground. The steady state impedance of the antiresonant circuit Cl3, L2, is about 200,000 ohms and is essentially resistive at its natural frequency. The impedance looking in at the mid-tap of inductance coil L2 is onequarter of this value or approximately 50,000 ohms. Accordingly, if RM, is matched to this approximately 50,000ohm impedance, one-half of the cathode voltage will be impressed across the upper half of the coil L2 (the upper terminal being connected through condenser C82 to ground). Due to the auto-transformer action between the upper half of coil L2 and the entire coil, the voltage at the lower terminal will be double that at the mid-tap of coil L2. n other words, a voltage equal to the cathode voltage is impressed upon the grid and the net gain of the feedback path is equal to unity and, when this condition exists, no rapid increase or decrease in amplitude of the timing wave can occur. The resistance of resistor RM may be varied until this unit gain is obtained. Since the timing wave is interrupted after about 11 cycles have been generated, a small departure from unity gain of the feedback path would not cause an appreciable change in amplitude.

The use of tube V3 and its associated circuit to provide feedback for the oscillatory circuit C13, L2, is a secondary one. The primary purpose of this circuit is to generate two waves of substantially equal amplitude which are accurately in quadrature with respect to each other starting substantially at the first instant of each wave train. A starting transient, lasting through a considerable fraction of a cycle of the timing wave, such as is produced with a simple resistance-capacity phase splitting circuit, is thus avoided.

The method of obtainin the quadrature voltages will be explained with reference to Figs. 6, '7, 8 and 9, each of which shows the cathode, control electrode and anode of electric discharge device V 3. The curves in each figure show the alternating component of the cathode potential Ex, which is, substantially the same as the grid potential EG, the current I through the anode-cathode path and the anode potential Er, all potentials being with respect to ground. In Fig. 9 the two components of current I, namely 10 and IR are also shown.

In Fig, 6 a resistance R is connected between the anode and the positive terminal of the anode voltage source (+3) the negative terminal of the anode voltage source being grounded in each case. A capacitance C is connected between the cathode and ground. The time to is the instant at which the current in the circuit of inductance L2 is interrupted to start the generation of the timing wave. The timin wave potential is impressed upon the grid in each case and it is assumed that the electronic tube has a mutual conductance so large that the difference between the grid potential EG and the cathode potential Ex is negligible. The current in the circuit is That is, EP is proportional to the derivative of Ex. In the absence of tube overloading, this relationship is true for both the steady-state timing wave and the discontinuity at time to. If in the steady state,

EK=A sin wt where w=21rf or approximately 6.28 times the frequency,

01 (A sin wt) d:

In order to make the amplitude of the anode potential wave equal to the cathode potential wave, R is made equal to i wC so that to Then E' %(wA cos wt) A cos wt EP and Ex are thus equal in amplitude but 90 degrees out of phase with respect to each other. This arrangement of Fig. 6 suffers from the fact that no unidirectional space current can flow in the circuit because the cathode is connected to ground only through a condenser, This dificulty can be obviated by connecting a high resistance or a high inductance path across the condenser C but such a modified circuit would cause the introduction of some phase error.

In the arrangement illustrated in Fig. 7, an inductance L is connected between the positive terminal of the unidirectional voltage source +B and the anode, and a resistance R is connected between the cathode and ground. In this case R and d1 L dE EP n it a If, as before,

EK=A sin wt LAw cos cot E,,-

I [E dt-kconstant of integration and E) IR i [Emit R (constant) When the cathode wave Ex starts as shown in Fig. 8, the constant in these expressions acquires a positive value equal to the peak value of the alternating component of current. The current starts up from zero as though from a negative peak in its cycle. If the current were to continue as a pure sinusoidal wave, an increased average current would be required. Since there is no change in the steady-state potentials on the tube electrodes to sustain an increased cur-- rent, the average value of the current wave returns to its original value exponentially with a time constant which may be shown to be equal to L multiplied by the mutual conductance of the tube.

It should be noted that if the timing wave potential at the grid and cathode were to start a quarter cycle earlier or later, that is, with an abrupt rise or fall of potential to maximum or minimum peak amplitude, the arrangement of Fig. 8 would become feasible because the constant of integration would equal zero, and the arrangements of Figs. 6 and 7 would acquire transient difficulties in that difierentiation of the steep wave front would tend to produce the overloading.

The arrangements of Figs. 6 and 7 can be com bined as shown in Fig. 9 so that the inductance L and resistance RP in shunt with respect to each other are connected between the anode and the positive terminal of the direct voltage source and resistance RK and capacitance C in shunt with respect to each other are connected between the cathode and ground. This is the arrangement which is specifically utilized in the range unit of Figs. 3, 4 and 5. In this case, if the current IRP through R)? equals the current In through C and if the current It through L equals the current IRK through Rx,

and

If, as before,

E =A sin wt and ;=R C=% then EP=A cos at In this embodiment resistance R1; provides a direct current path from the cathode to ground and resistance RP critically damps the undesired oscillations which would be generated due to the shock-excitation of the inductance L if the damping were omitted. In the circuit arrangement shown in Fig. 3, the cathode resistance R11; is made up effectively of resistors R15, R19 and twice the resistance of RM, all in parallel, since each is an alternating current path between the cathode and ground. Twice the resistance of RM is effectively in the circuit because of the impedance of the tuned circuit L2, GB. The screen grid capacitor Cll' is returned to the cathode in order that the same alternating current may flow through the anode and cathode imped ances. The cathode potential of tube V3 is such with respect to the control grid potential that the grid current is zero at all times. By varia tion of trimmer condenser CIB in the cathode circuit, it is readily possible to adjust the oathode and anode voltages to exact quadrature. The

amplitudes of these voltages are then equal if the inductance of LI has the correct value in relation to the plate and cathode resistances.

In some cases it may be desirable to employ a continuous wave rather than an intermittent wave for the control grid potential EG in which case no difi'iculty will be experienced due to parasitic oscillations or startin transients as discussed above in connection with Figs. '7 and 8. Moreover, it may :be desirable in some cases to employ a potential wave Es other than a sine wave. When any variable potential is impressed upon the control electrode, there will be produced at the cathode and anode electrodes, respectively, varying potentials one of which is proportional to the derivative of the other, within the obvious limitations imposed by stray capacitances, tube overloading, and the constant of integration in the case of the circuit of Fig. 8.

There are provided two phase inverter triodes V4.1 and V2.2 each for impressing upon opposite sector stator plates of a phase shift condenser C25 timing wave potentials which are 180 degrees out of phase with respect to each other. The anode current path for triode V2.1 may be traced from 300-volt source through resistor R24, mono-011m resistor R23, the anode-cathode path, 1,500-ohm resistor R22 and 10,000-ohm resistor RM to ground. The control grid of this triode is connected through l-megohm resistor R28 to the common terminal of resistors R2! and R22. The anode current path for triode V l.2 may similarly be traced from the EGO-volt source through resistor R24, 10,000-ohm resistor R28, the anodecathode path, 1-500-ohm resistor RH, and 10,000-ohm resistor R25 to ground. One-megohm resistor R26 connects the control grid to the common terminal of resistors RH and R25. A 0.1- microfarad condenser CB3 provides a low impedance path from the negative terminal of resistor R24 to ground. The cathode of tube V3 is connected through 0.01-microfarad condenser Cl8 to the control grid of triode V M and the anode of tube V3 is connected through 0.0l-microfarad condenser CH) to the control grid of triode V4.2.

The mutual conductance of each of the triodes V4.l and V4.2 is sufiiciently large to cause the cathode potential of each to be an accurate copy of the potential of the corresponding control electrode. As the same current passes through R23 and R2I, by way of the anode-cathode path of V4.l, the anode potential of V41 is equal in amplitude to the potential at the junction of RH and R22, but 180 degrees out of phase therewith. Similarly, the anode potential of V5.2 is equal in amplitude to, but 180 degrees out of phase with, the potential at the junction of R25 and R21. In view of the phase relationship established in the circuit of V3, it may be seen that the four last-mentioned potentials are alike in amplitude, but that three of them diiier in phase from the fourth by 90 degrees, 180 degrees and 270 degrees, respectively, this relationship being established at essentially the first instant of each timing wave train.

The phase shifter condenser C25 comprises a metallic ring 86, four metallic stator sectors 8 l, 82, 83 and 84 and a dielectric rotor ill of a material having a dielectric constant considerably different from that of air. The phase shifter condenser is described in detail in my copending application, supra. The stator sector 8| is connected to the common terminal of resistor R23 and the anode of tube 41; stator sector 33 is connected to the common terminal of resistors R2! and R22; stator sector 82 is connected to the common terminal of resistor R28 and the anode of tube and stator sector 8% is connected to the common terminal of resistors R25 and R21. Condense-rs C23 and 024 each of 10 micromicrofarads are connected between stator sectors 8! and 82, respectively, and ground. Variable 25-micromicrofarad condensers C2! and C22 are connected between stator sectors 33 and 8d, respectively, and ground, these condensers being variable to allow for accurate balancing of the cathode and anode reactances.

The ring stator of the phase shifter is connected by lead 89 to the input of a two-stage amplifier comprising electronic tubes V5 and V5 and the output of the amplifier is connected to a timing pulse generator circuit comprising electronic tubes V7 and V3. The lead 32 is connected through lOO-ohm resistor R33 to the control grid of the tube V5. Anode potential is supplied to the tube from BOO-volt source 5! through LOGO-ohm resistor R35 and l0,000-ohm resistor R35, the anode-cathode path, l80-ohm resistor R32 and 1,000-ohm resistor R3! to ground. Control grid biasing potential is provided due to anode current flowing through resistor R32, which bias is applied to the grid through 0.1-megohm resistor R29 and 0.4'7-megohrn resistor R30 in series. A 0.01- microfarad condenser C2? connected from the common terminal of resistors R29 and R30 to the cathode of tube V5 by-passes alternating components of the voltage across R32. Screen grid voltage is supplied to tube V5 through resistor R36, 68,000-ohm resistor R31 and -ohm resistor RM, the common terminal of resistors R31 and R34 being connected through 0.0l-rnicrofarad condenser C29 to the cathode. Condenser C26 of 0.1 microfarad is connected between ground and one terminal of resistor R36 to suppress voltage variations of the 300-volt source. The anode of V5 is connected through 0.01-microfarad condenser C28 and 100-ohm resistor R40 to the control grid of amp-lifiertube V6. Anode voltage is supplied to tube V6 from the 300-volt source through resistor R36, 10,000-ohm resistor RM, the anode-cathode path and ISO-ohm resistor R4! to ground. A 0.1 megohm resistor R38 is connected from the common terminal of condenser C28 and resistor RM! to ground. Screen grid voltage is supplied from the 300-volt source through resistor Rte, 68,000-ohm resistor RM and l00-ohm resistor RM, the common terminal of resistors R44 and R42 being connected through 0.01-microiarad condenser C3! to the cathode. Negative feedback is provided by connecting the anode of tube V5 through 0.1 megohm resistor R39 to the cathode of tube V5.

The amplified timing wave voltage at the anode of tube Vt is impressed through 0.01-microfarad condenser C30 and 100-ohm resistor R46 upon the control grid of the center clipper tube V! of the timing pulse generator 22. The common terminal of resistor R 38 and condenser C30 is connected through 0.1megohm resistor R45 to ground and the tube cathode is connected through 10,000-ohm resistor Rdl shunted by 50-micromicrofarad condenser C33 to ground. Anode voltage is supplied to tube V! from the 300-volt source through 1,000-ohm resistor R53 and 18,000-ohm resistor R42, and screen grid voltage is applied through 100-ohm resistor R50 from the voltage divider formed by 33,000-ohm resistor R5I and 33,000-ohm resistor R52, the common terminal of resistors RM and R52 being connected through "13 l mi'crofarad condenser C34 to the cathode. Tube V! acts as a cathode follower during the positive half cycles of the timing wave impressed upon its grid and is out 01f during the negative half cycles. During the positive half cycles on the .grid, when the grid potential first increases and then decreases, the anode potential first decreases and then increases. While the tube is cut ofi the anode potential is constant. The anode of tube V! is connected through 150-micromicrofarad condenser C35 and l-ohm resistor R56 to the control grid of tube V0, the cathode of 'which is grounded. Anode voltage is supplied to tube V8 through resistor R53 and 1,500-ohm reisistor R51. Screen grid voltage is supplied from the 300-volt source through resistor R53, 0.1- megohm resistor R59 and 100-ohm resistor R53, the "common terminal of resistors R59 and R58 being-connected through 0.1-microfarad condenser 0322 to round. Condenser C325 of 0.1-microfar-ad is connected between the negative terminal of resistor R53 and ground. The cathode of tube V! is made positive with respect to ground due to the connection of the cathode to the common terminal of the voltage dividing resistors R41 and R48 (1.8 megohms). The grid of tube V8 is biased positively due to its connection to the common terminal of the voltage dividing resistors R54 and R55 (1 megohm). During the quiescent periods when no wave is being generated by the timing Wave generator, grid current flows in tube V8 and the grid is at a slightly positive potential. During the active periods when the timing wave is being generated, the change in anode potential of tube V1 causes the grid potential of tube V8 to be sharply decreased at the beginning of one-half cycle of the timing wave and to be sharply increased at the "beginning of the following half cycle so that conduction in tube V8 is cut ofi and restored alternately. The resulting square wave at the anode of tube V8 is differentiated by means of loo-micromicrofarad condenser C36 and 1,500-ohm resistor R61, which elements are connected in series between the anode of tube V8 and ground, to produce alternately positive and negative sharp pulses across resistor R61.

The pulse selector 23 comprises a triode electronic device Vl.2 and a pentode electronic device VIO. Anode current is supplied to tube V1. 2 from the BOO-volt source through 1,- 000-ohm resistor R13 and 1-megohm resistor R62, the cathode being grounded. The common terminal of resistors R73 and R52 is connected through l-megohm resistor R50 to the control electrode. There is provided a con-denser charging circuit having a time constant of about BOO-microseconds which may be traced from the positive terminal of the 300-volt source through resistors R13, R62, 750-micromicrofarad condenser C38, shunted by IOO-micromicrofarad. variable condenser C39, and 1,500-ohm resistor R6! to ground. The common terminal of resistor R62 and condenser C38 is connected through 100- ohm resistor R03 to the control electrode of tube V The anode current path for this tube comprises resistor R13, 1.8-megohm resistor R64, the anode-cathode path, a variable portion of the resistance of 20,000-ohm potentiometer R67 and "680-ohm resistor 87 to ground, the cathode also being connected through 0.003-microfarad cond'e'nserC lfl to ground. The cathode potential may be varied by moving the variable tap of potentiometer R61, this potentiometer being in a series circuit which may be traced from the 300-volt source through resistor R13, 40,000-o'hm resistor R68, potentiometer R61 and resistor R8! to ground. Screen grid potential is supplied from the common terminal of voltage dividing resistors R10 (47,000 ohms) and R69 (0.1 megohm) through -ohm resistor R65. Resistor R69 is shunted by 100-micromicrofarad condenser C42. The square wave 0 from start-stop generator I6 is impressed upon the control grid of tube VLZ through lead 60. During the quiescent periods when the start-stop wave is positive, the grid of tube V|.2 is positive, grid current being drawn through resistor R60. As a result the anodecathode resistance of the tube is low and the anode potential is reduced nearly to ground potential (about +1.1 volts). When the tube Vl.2 is cut ofi due to the negative portions I 1 of startstop wave 0, condenser C38 and its trimmer C39 are charged through resistor R62 to a potential which rises exponentially toward a 300-vo1t asymptote. The alternately positive and negative timing pulses which appear across the resistor R6! are applied in series with the expon'e'ntially rising condenser voltage to the control grid of tube V-lfl.

selection of one of the timing pulses of each group of pulses is controlled by varying the setting of potentiometer R67 to vary the cathode potential of tube V-lil. The first pulse (28) of each group of pulses which raises the grid potential of tube Vl0 sufiiciently with respect to the cathode potential to cause anode current to flow may be designated as the selected pulse since it causes the potential at the anode of tube VI!) to drop sharply to control the production of a corresponding range pulse. If the setting of potentioinetei' R0? were varied progressively without varying the setting of the phase shifter condenser C25, the interval between the radiated pulses b and the corresponding selected pulses or range pulses 26 would vary in steps, the interval of each step corresponding to approximately 12.2 microseconds or a range of 2,000 yards. By coupling potentiometer shaft 34 to the shaft 29 of the phase shifter condenser by means of gears 24, the interval between the radiated pulses and the corresponding selected pulses or range pulses may be varied continuously. The resistance winding of the potentiometer R67 is preferably non-uniformly distributed to correct for the curvature of the exponentially rising voltage across the condensers C38 and C39 so that a change in cathode potential corresponding to a single revolution of the potentiometer shaft 29 will be equal to the potential difference at the grid of tube Vii! between the peak potential of a timing pulse which is to be selected and the peak potential of a succeeding positive timing pulse at any time during each active interval. Instead of superposing the timing pulses upon the exponentially rising control grid potential of tube Vl0, they may be superposed upon the cathode potential of tube V10 by connecting one plate of each of condensers C38 and C39 directly to ground, connecting the lead from condenser 036 to the cathode of tube V40 and connecting a resistor between the cathode of tube Vin and condenser C40. In this case one of the negative timing pulses is selected.

here is provided an output amplifier comprising electronic devices V9.2 and V! l which repeats the selected pulses or range pulses and which sup presses the timing pulses following each of the selected pulses. The anode of tube V10 is connected vthrough .0005-mic-rofarad condenser CM 15 and l.8-megohm resistor Rll in series to ground and the control grid of tube VE.2 is connected to the common terminal of condenser Cil and resistor Rll. The anode current path of this tube may be traced from the positive terminal of the 300-vol-t source through resistor RYE, 22,00o-ohm resistor R12, the anode-cathode path and M9- ohm biasing resistor 82 to ground, the resistor R552 being shunted by 0.0l-microfarad condenser Filter condenser C323 of 0.1 microfarad is connected between the common terminal of resistors R13 and R12 and ground. The anode of tube 9.2 is connected through ldil micromicrofarad condenser CM and 0.1-rnegohm resistor RM in series to ground and the common terminal of the condenser and resistor is connected through 100- ohm resistor RTE to the control grid of tube Vi i. Positive biasing potential is provided for the oathode of tube V ll by connecting it to the common terminal of the potential dividing resistors Bid (0.22 megohm) and R (15,000 ohms) which are connected in series between the negative terminal of resistor R73 and ground, the resistor R15 being shunted by 0.01-microfarad condenser C46. Anode potential is supplied to tube VII from the 300-volt source through resistor R'i3 and 33,000- ohm resistor R18. Screen grid voltage is also supplied from the 300-volt source through resistor R13, 18,000-ohm resistor R80 and IOU-ohm resistor R79, the common terminal of resistors R19 and R80 being connected through 0.0005- microfarad condenser C4! to ground. The anode of tube Vll is connected through 0.002-microfarad condenser C48 and 1,800-ohm resistor Rdi in series to ground. The primary winding of output transformer TI is connected across resistor RBI to cause the production of range pulses 2' across the secondary winding one terminal of which is grounded.

When tube V10 becomes conducting due to a positive timing pulse which is superposed upon the exponentially rising grid potential, the potential at the anode of tube Vii! is reduced and condenser C4! discharges through a circuit comprising the anode-cathode path of tube Vii] and resistor R'll. Tube V9.2 which norm-ally conducts is thus cut off and remains out 01f due to the voltage drop across resistor R7! during the remainder of the active period and the timing pulses which follow the selected pulse are thus not repeated. The interruption of conduction through tube 9.2 due to the selected timing pulse causes the production of a positive pulse at the control grid of tube Vi i causing it to pass extremely large anode current momentarily, thus producing a negative pulse at the anode of tube VI l. The resulting range pulse at the secondary of transformer TI may obviously be of either positive or negative polarity as desired. If de-- sired, moreover, this output pulse may be utilized to generate a step as disclosed in my copending application, supra. A negative pulse is also produced at the common terminal of resistors Riiil and R19 to cause -micromicrofarad condenser C45 to discharge through a path including the screen grid-cathode path of tube Vii and resistor RN to reinforce the negative potential at the grid of tube V9.2 so that tube V9.2 is cut off very sharply and remains so until the end of the active period.

While triodes VM and Vi.2 are shown as individual tubes, these triodes may be within a single evacuated envelope since the triodes are cut off and restored. in synchronism. Triodes V9.l and V9.2 may also be within a single evacu- Tail 16 ated envelope. Triodes VI.2 is not placed within the same envelope with triode V9.2 since cut off of triode tube V1.2 would not be complete while triode V9.2 is conducting.

The cathode ray device 38 comprises, in addition to the vertical and horizontal deflecting plates, a cathode H0, anodes I20 and a phosphorescent screen E23. The sweep wave it produced by the sweep circuit 35 and applied to the deflecting plates 33 causes the cathode ray beam to sweep across the screen repeatedly in a horizontal direction, for example. The range pulses 26 from the output transformer TI of the range unit are applied to one of the vertical deflecting plates 35 of the cathode ray tube to cause the production of a vertical deflection in one direction upon the screen I23 and the echo pulses 7' from the radio receiver l3 are applied to the other vertical deflecting plates 3| to produce a vertical deflection of the cathode ray beam in the opposite direction. By rotating the shaft 29 of the phase shifting condenser C25 of the phase shifter and the shaft 34 of the potentiometer R6? of the pulse selector by means of a handle E25, the visual indication produced by the range pulses 26 may be caused to travel across the screen 523 and brought into alignment with the visual indication produced upon the screen by the echo pulses i. The distance to the object from which the echo pulses are received may then be read directly upon the revolution counter or distance indicator 32 which is calibrated in units of distance, each complete revolution of the shaft 29 changing the delay of the range pulses 25 with respect to the corresponding transmitted pulses b by an interval corresponding to 2,000 yards.

In some cases it may be desirable to produce pulses which are delayed with respect to corresponding starting pulses a by impressing only the start-stop wave 0 upon the pulse producing circuit comprising electronic devices Vl.2 and Vic, the amount of delay being controlled by the setting of potentiometer R61 and the time constant of the condenser charging circuit comprising resistors Bill and R62 and condensers C38 and C39.

What is claimed is:

l. The combination with a space current device having a cathode, an anode and a current control electrode, of a source of potential difference for causing space current to flow between said anode and cathode, a filter current path connecting said cathode and said control electrode comprising a first impedance means having a first terminal conductively connected to said cathode and a second terminal, a second path comprising a second impedance means which path is between said anode and said second terminal of said first impedance means, the vector impedances of said two impedance means being equal in magnitude and having a -degree angle therebetween, and means for impressing upon said first current path a sine wave voltage having a certain frequency for setting up an alternating component voltage between said anode and said second terminal and a second alternating component voltage between said cathode and said second terminal which component voltages are similar in amplitude and wave form and 90 degrees out of phase with respect to each other, one of said impedance means comprising a first resistor and a capacitive reactance element connected in parallel and the other of said impedance means comprising a second resistor and an inductive reactance element connected in parallel, the resistance of said first resistor being equal to the reactance of said inductive element and the resistance of said second resistor being equal to the reactance of said capacitive element at the frequency of said sine wave.

2. The combination in accordance with claim 1 in which are provided a second and a third space current device each having a cathode, an anode and a control electrode, impedance paths for connecting the anodes and the cathodes, respectively, of said second and third devices, respectively, to said second terminal, means for causing anode currents to fiow in the anodecathode paths of said second and third devices, means for connecting the anode of said first device to the control electrode of said second device and means for connecting the cathode of said first device to the control electrode of said third device for causing the production at terminals connected to said anode and cathode impedance paths, respectively, of said second and third devices with respect to said second terminal alternating component voltages which are similar in amplitude and wave form and three of which are out of phase with respect to the fourth by 90 degrees, 180 degrees and 270 degrees, respectively.

3. In combination, an electronic device having an anode, a cathode and a control electrode, a source of unidirectional voltage for causing space current to flow in a circuit including the anodecathode path of said device, a first impedance means comprising inductance and resistance in parallel with respect to each other, a second impedance means comprising capacitance and resistance in parallel with respect to each other, one of said impedance means being connected between said anode and said voltage source and the other of said impedance means being connected between said cathode and said voltage source, a varying voltage source, and a circuit comprising said varying voltage source connecting said control electrode and a terminal of said unidirectional voltage source to produce across said first and second impedance means, respectively, varying voltages one of which is proportional at every instant to the derivative of the other, the ratio of said resistance of said first impedance means to the reactance of said inductance of said first impedance means being equal to the ratio of the reactance of said capacitance of said second impedance means to said resistance of said second impedance means.

4. The combination in accordance with claim 3 in which are provided a second and a third electronic device each having an anode, a cathode and a control electrode, two paths each comprising a. resistor for connecting the anodes of said second and third devices, respectively, to said unidirectional voltage source, two paths each comprising a resistor for connecting the cathodes of said second and third devices to said unidirectional voltage source, capacitive means for coupling the anode of said first device to the control electrode of said second device, and capacitive means for coupling the cathode of said first device to the control electrode of said third device.

5. In combination, an electronic device having an anode, a cathode and a control electrode, a series circuit comprising the portion of said device between said anode and said cathode, a source of anode current in said circuit, a first impedance means having inductive reactance shunted by resistance, a second impedance means having capacitive reactance shunted by resistance, one of said impedance means being connected between said anode and said current source and the other of said impedance means being connected between said cathode and said current source, input terminals between which are said other of said impedance means and the portion of said electronic device between said cathode and said control electrode, means for applying to said input terminals a sine wave voltage having a certain frequency, the resistance in shunt with said inductive reactance being equal to said capacitive reactance and the resistance in shunt with said capacitive reactance being equal to said inductive reactance, and two sets of output terminals which are effectively across said first and said second impedance means, respectively, there being a path of substantially negligible impedance connecting said first and second impedance means, whereby there are produced across said output terminals respectively sine wave voltages similar to said input voltage but which are degrees out of phase with respect to each other.

6. A combination in accordance with claim 5 in which there is applied to said input terminals an intermittent sine wave voltage for producing two intermittent sine wave output voltages, one of which is proportional at every instant to the derivative of the other.

7. In combination, a space current device having an anode, a cathode and a control electrode, a source of variable potential difference, a source of space current for said device, a first impedance means comprising inductance and resistance in parallel, a second impedance means comprising capacitance and resistance in parallel, the ratio of said inductance in henries to said capacitance in farads being substantially equal to the product of said resistances in ohms, a first circuit connecting said anode and said cathode comprising in series said source of space current and said first and second impedance means, a second circuit connecting said control electrode and said cathode comprising one of said impedance means and said source of variable potential difierence, and means for utilizing the potential difierences across said first and second impedance means, respectively.

LARNED A. MEACHAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,124,973 Fearing July 26, 1938 2,231,955 Schrader Feb. 18, 1941 2,324,797 Norton July 20, 1943 2,332,253 Peterson Oct. 19, 1943 FOREIGN PATENTS Number Country Date 516,358 Great Britain 1939 OTHER REFERENCES Frequency Modulation, by August Hund, Mc- Graw-Hill Book Co., 1942, page-187. 

